TAILIEUCHUNG - Ebook Engineering mechanics - Statics (12th edition): Part 2

(BQ) In addition to over 50% new homework problems, the twelfth edition introduces the new elements of conceptual problems, fundamental problems and mastering Engineering, the most technologically advanced online tutorial and homework system. | Internal Forces CHAPTER OBJECTIVES To show how to use the method of sections to determine the internal loadings in a member. To generalize this procedure by formulating equations that can be plotted so that they describe the internal shear and moment throughout a member. To analyze the forces and study the geometry of cables supporting a load. Internal Forces Developed in Structural Members To design a structural or mechanical member it is necessary to know the loading acting within the member in order to be sure the material can resist this loading. Internal loadings can be determined by using the method of sections. To illustrate this method consider the cantilever beam in Fig. 7-1 . If the internal loadings acting on the cross section at point are to be determined we must pass an imaginary section - perpendicular to the axis of the beam through point B and then separate the beam into two internal loadings acting at B will then be exposed and become external on the frec-lxxly diagram of each segment. Fig. 7-1 . a Fig. 7-1 330 Chapter 7 Internal Forces In each ease the link on the backhoe is a two-force member. In the top photo it is subjected to both bending and an axial load at its center. By making the member straight as in the bottom photo then only an axial force acts within the member. b ig. 7-1 lie force component Ng that acts perpendicular to the cross section is termed the normal force. Tile force component Vg that is tangent to the cross section is called the shear force and the couple moment Mg is referred to as the bending moment. The force components prevent the relative translation between the two segments and the couple moment prevents the relative rotation. According to Newton s third law. these loadings must act in opposite directions on each segment as shown in Fig. 7-1 . They can be determined by applying the equations of equilibrium to the frec-body diagram of either segment. In this case however the right segment is the better

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